VPRN Service Overview
Page 1052 7750 SR OS Services Guide
BGP Support
BGP is used with BGP extensions mentioned in Routing Prerequisites on page 1051 to distribute
VPRN routing information across the service provider’s network.
BGP was initially designed to distribute IPv4 routing information. Therefore, multi-protocol
extensions and the use of a VPN-IPv4 address were created to extend BGP’s ability to carry
overlapping routing information. A VPN-IPv4 address is a 12-byte value consisting of the 8-byte
route distinguisher (RD) and the 4-byte IPv4 IP address prefix. The RD must be unique within the
scope of the VPRN. This allows the IP address prefixes within different VRFs to overlap.
eiBGP Load Balancing
eiBGP load balancing allows a route to have multiple nexthops of different types, using both IPv4
nexthops and MPLS LSPs simultaneously.
Figure 126 displays a basic topology that could use eiBGP load balancing. In this topology CE1 is
dual homed and thus reachable by two separate PE routers. CE 2 (a site in the same VPRN) is also
attached to PE1. With eiBGP load balancing, PE1 will utilize its own local IPv4 nexthop as well as
the route advertised by MP-BGP, by PE2.
Figure 126: Basic eiBGP Topology
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